Note: Descriptions are shown in the official language in which they were submitted.
Method and Apparatus for Integrating
Components of a Refrigeration System
This invention in general relates to refrigeration circuits and a
method of operation thereof. More particularly, this invention
relates to refrigeration circuits and components wherein a
condenser designed to operate as a portion of a high efficiency
refrigeration circuit is paired with an evaporator designed to
operate as a portion of a lower efficiency refrigeration circuit.
In a typical residential air conditioning application, a condenser
is mounted in heat exchange relation with ambient air and an
evaporator is mounted in heat exchange relation with the air of
the enclosure to be conditioned. A compressor and an expansion
device are joined with the condenser and evaporator to form a
refrigeration circuit such that heat energy may be transferred
between the enclosure air and ambient air.
As the cost of energy to operate an air conditioning system has
increased, the manufacturers of air conditioning equipment have
attempted to produce more energy efficient equipment. This change
in energy efficient equipment has resulted in certain operational
characteristic changes between earlier produced equipment and
newer higher efficiency equipment.
One of the ways of achieving higher efficiency in an air
conditioning system is to decrease the head pressure and
consequently the condensing pressure.
In a typical residential air conditioning installation, the
components of the refrigeration system perform for their useful
life and then need to be replaced. Other components, often the
indoor heat exchanger, may have a longer useful life and may
continue to perform satisfactorily although the other components
need to be replaced. This partial replacement may result in the
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compressor and condenser being replaced and the evaporator
remaining from the original system.
The energy conscious consumer often desires to replace a portion
of a system with newer higher efficiency equipment. The
utilization of this higher efficiency equipment, however, presents
a problem when it is combined with the evaporator from a
refrigeration system having capillary tubes as expansion devices.
The mating of refrigeration circuit components being designed to
operate at different head pressures may result in a decreased
capacity of the system, lowering the overall efficiency of the
system and/or other operational problems. The severity of these
problems depend upon various factors including the expansion
device associated with the indoor heat exchanger and the sizing of
interconnecting piping. Oftentimes an expansion device of a
residential size evaporator comprises a series of fixed diameter
capillary tubes.
Capillary tubes which are often used as the expansion devices in a
residential size evaporator act to reduce the pressure of
refrigerant flowing therethrough. These capillary tubes are sized
to allow a predetermined mass flow rate at a given temperature and
head pressure. If the head pressure is reduced the mass flow rate
through the capillary tube may also be reduced. However, should
the temperature of the refrigerant flowing through the capillary
tube be reduced, the mass flow rate may increase since the
viscosity of liquid refrigerant decreases as it is further
subcooled.
The present refrigeration system and components are designed to
provide an efficient refrigeration circuit having a replacement
component designed to operate at a lower head pressure than the
existing component to which it is to be matched.
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Prior art devices incorporating subcoolers and intermediary heat
exchangers are known in the art. The present invention utilizes
an intermediate heat exchanger as a flash subcooler such that a
portion of the liquid refrigerant circulating from the condenser
to the evaporator is diverted to the intermediate heat exchanger
wherein it is flashed to the compressor suction pressure. As the
refrigerant changes state from a liquid to a gas it absorbs heat
energy from the refrigerant flowing from the condenser to the
evaporator subcooling same. Hence, the flow rate of refrigerant
flowing through the condenser is different from the flow rate
through the evaporator. However, the diverted portion of the
refrigerant is not wasted since the heat energy that may have been
absorbed upon the flashing of that refrigerant in the evaporator
is used to further subcool the refrigerant entering the
evaporator.
According to the preferred embodiment of the present invention
there is provided an intermediate heat exchanger located to have
at least a portion of the refrigerant flowing from the condenser
to the evaporator passing through a first flow path of the
intermediate heat exchanger. Means are provided to divert a
portion of the refrigerant flowing from the condenser to the
evaporator to a second flow path of the intermediate heat
exchanger wherein the diverted portion of the refrigerant is
placed in heat exchange relation with the refrigerant flowing
through the first flow path of the heat exchanger. ~urthermore,
tubing is provided to connect the second flow path of the heat
exchanger to the compressor suction line such that a flow path for
the diverted refrigerant to be returned to the compressor is
provided therethrough.
A thermal expansion valve is connected to regulate the flow rate
of refrigerant diverted to the second flow path of the
intermediate heat exchanger. A temperature sensing bulb of the
thermal expansion device is mounted to sense the temperature of
the refrigerant flowing from the evaporator to the compressor and
to regulate the flow that is diverted as a function thereof. An
equalizing line is provided between the compressor suction line
and the thermal expansion valve to balance the thermal expansion
valve.
This invention will now be described by way of example with
reference to the accompanying drawing in which Figure 1 is a
schematic diagram of a refrigeration circuit incorporating the
present invention; Figure 2 is an isometric view of a subassembly
including the heat exchanger and thermal expansion valve; Figure 3
is a schematic plan view of a residential air conditioning system
including an indoor unit and an outdoor unit; and Figure 4 is a
schematic view of a portion of a refrigeration circuit showing
another embodiment of the present invention.
The embodiments hereinafter described will refer to a
refrigeration circuit for use in an air conditioning system. It
is to be understood that the invention herein has like
applicability to refrigeration and applications other than air
conditioning. The preferred embodiment herein is further
described as applying to a residential application wherein the
various components have certain flow rate characteristics. This
invention is not limited to this application nor to the
characteristics of the components replaced or the components mated
therewith.
The invention herein is described having a particular heat
exchanger for accomplishing heat transfer between the various
refrigerant flows. The choice of a heat exchanger is that of the
designer as may be the choice of expansion apparatus and o-cher
interconnecting means.
In a conventional vapor compression refrigeration circuit gaseous
refrigerant has its temperature and pressure increased by the
compressor and is then discharged to the condenser wherein heat
energy is discharged and the gaseous refrigerant is condensed to a
liquid refrigerant. The liquid refrigerant then undergoes a
pressure drop in the expansion device such that liquid refrigerant
may vaporize to a gas in the evaporator absorbing heat energy from
fluid to be cooled. The gaseous refrigerant is then returned to
the compressor to complete the refrigeration circuit.
Referring first to Figure 1 there may be seen a schematic view of
a refrigeration circuit incorporating the present invention.
Compressor 30 is shown having compressor discharge line 22
connected to condenser 20. Interconnecting line 16 connects
condenser 20 to expansion device 12. Line 14 connects expansion
device 12 to evaporator 10 which is connected by compressor
suction line 32 to compressor 30.
Flash subcooler 50 is shown in Figure 1 having interconnecting
line 16 running therethrough. Flash subcooler 50 includes thermal
expansion valve 52 connected by thermal expansion valve feed line
62 to interconnecting line 16. Thermal expansion valve discharge
line 66 connects the thermal expansion valve to flash chamber 56
of the flash subcooler. Subcooler suction line 34 connects the
flash chamber to the compressor suction line 32. Thermal
expansion valve equalizer line 64 additionally connects thermal
expansion valve 52 to the compressor suction line 32 via subcooler
suction line 34.
Bulb 54 of the thermal expansion valve is connected by capillary
55 to the thermal expansion valve. The bulb is mounted on the
compressor suction line to sense the temperature of the
refrigerant flowing from the evaporator to the compressor.
Referring now to Figure 2, there may be seen an isometric view of
the flash subcooler 50. A casing 58 is provided which may be
insulated (not shown) and has the thermal expansion valve and
various co~mections therein. Interconnecting line 16 is shown
forming a first flow path of the heat exchanger. The outside
surface of interconnection line 16 and outer tube 72 form a second
flow path of the heat exchanger. The space therebetween is
designated as flash chamber 56. Refrigerant flow from
interconnecting line 16 may be diverted to the thermal expansion
valve through thermal expansion valve feed line 62. The
refrigerant flowing through line 62 passes to the valve and is
discharged from the thermal expansion valve to line 66. Thermal
expansion valve line 66 may be a simple tube or it may be a
capillary tube to further limit the flow of refrigerant
therethrough and to smooth out the fluctuations of $he thermal
expansion valve. As used herein the expansion device will refer
to either the thermal expansion valve solely or the combination of
capillary tubes connected to the discharge of the thermal
expansion valve.
It is further seen in Figure 2 that bulb 54 of the thermal
expansion valve is connected by capillary 55 thereto. The bulb is
mounted on the compressor suction line 32 to sense the temperature
of the refrigerant flowing therethrough. Refrigerant from the
thermal expansion valve is supplied through the tube 66 to
connector 74. From connector 74 the refrigerant flows through
flash chamber 56 to connector 76. The refrigerant then flows
through connector 76, through tee 78 and through subcooler suction
line 34 to the compressor suction line. Thermal expansion valve
equali7ing line 64 is also shown connected to tee 78 and to the
thermal expansion valve.
In Figure 3 there can be seen a typical application of this
subcooler to a residential air conditioning system. Outdoor heat
exchanger 86 is shown having service valves 85 and 88 to make
connections to the indoor heat exchange unit 82. The indoor unit,
shown within enclosure wall 80, is located in the basement or
otherwise within the enclosure to be conditioned and has a blower
assembly 84 for circulating air and a heat exchanger located
within the indoor heat exchange unit 82. Interconnecting tubing
designated as interconnecting line 16 and compressor suction line
32 are also shown.
It can be seen in Figure 3 that subcooler 50 is connected by
replacing a portion of interconnecting line 16 with the flash
subcooler assembly. It can be seen that connectors are provided
at both ends of the assembly such that they may be connected to
service valve 85 and to interconnecting line 16. The temperature
sensing bulb of the thermal expansion valve is shown as it is
fastened to compressor suction line 32. Additionally, the
subcooler suction line 34 is shown connected to service valve 88
through a shrader tee 89. A cap 91 is also located in the shrader
tee such that a closed refrigeration circuit is provided and that
refrigerant may be bled into or taken from the system through the
port. Hence, as can be seen in Figure 3 the utilization of this
subcooler assembly requires a subcooler line being attached to the
shrader tee, a thermal expansion valve bulb being connected to the
suction line and the heat exchange portion of the subassembly
being substituted for a portion of interconnecting line 16.
Figure 4 shows a separate embodiment of a subcooler assembly.
Therein there can be seen interconnecting line 16 which is formed
to include heat exchanger ]8 within flash chamber 56 of the unit.
Refrigerant flowing from the condenser flows through
interconnecting line 16 through the coil 18 and is then discharged
through line 16 to the evaporator. Line 62 connects line 16 to a
fixed orifice expansion device 53. Fixed orifice expansion device
53 is connected to the flash chamber such that liquid refrigerant
from line 16 may enter same and be flashed. Subcooler suction
line 34 connects the flash chamber to the compressor suction line
such that a closed circuit is formed for the flow of refrigerant
through line 62, to the expansion device, flash chamber and
finally to the compressor.
Other configurations of the flash subcooler might include coiling
the tube in tube heat exchanger into a helical configuration such
that the entire heat exchanger is located within casing 58. Also J
the thermal expansion valve may be located between the condenser
and the heat exchanger rather than between the heat exchanger and
the evaporator.
During operation of the various components herein hot condensed
liquid refrigerant from the condenser flows through
interconnecting line 16 to the evaporator. A portion of this
liquid is diverted through the thermal expansion valve feed line
62 to the thermal expansion valve. This refrigerant flow through
the feed line is regulated by the expansion valve and directed to
flash chamber 56 wherein it vaporizes absorbing heat energy from
the refrigerant flowing through interconnecting line 16. This
flashing of a portion of refrigerant acts to subcool the remaining
liquid refrigerant which is then conducted to expansion device 12
and to the evaporator where it absorbs heat energy from the fluid
to be cooled. By subcooling the liquid refrigerant the capacity
of a given flow rate to absorb heat energy in the evaporator is
increased. The flashed refrigerant in the flash chamber is drawn
through the subcooler suction line 34 to the compressor suction
line 32. Hence, both the flashed gaseous refrigerant from the
evaporator and from the flash chamber are drawn at the same
suction pressure to the compressor.
Thermal expansion valve 52 is a conventional valve having a
diaphragm whose position is regulated as a function of some other
temperature. In this instance, it is the temperature of the
compressor suction line which acts to regulate the flow to the
flash chamber. When the temperature of the compressor suction
line increases it indicates that the flow rate of refrigerant to
the evaporator is insufficient and that the refrigerant flowing
from the evaporator is superheated to a point where system
efficiency is decreased. hence, the thermal expansion valve will
increase the flow of refrigerant to the flash subcooler such that
the refrigerant flowing to the evaporator is further subcooled and
the mass flow rate of refrigerant through the capillary tubes will
increase.
If the temperature sensing bulb ascertains that the temperature of
the refrigerant flowing from the evaporator is too low it is an
indication that too much refrigerant is being supplied to the
evaporator. The low temperature may reflect a high flow rate such
that there is an insufficient opportunity to transfer heat energy
from the refrigerant in the evaporator to the air flowing
thereover. Under these circumstances, the thermal expansion valve
will act to decrease the flow of refrigerant diverted from
interconnecting line 16 such that flow is decreased to the
evaporator. The decrease of flow through the thermal expansion
valve will decrease the subcooling of the refrigerant flowing
through interconnecting line 16. The low termperature discharge
situation is to be carefully avDided to prevent liquid refrigerant
from being cycled to the compressor.
When a condensing unit of a refrigeration circuit including a
compressor having a first head pressure is replaced by a
condensing unit designed to operate at a lower head pressure it is
necessary to integrate the components of the refrigerant circuit
since they may have different design pressures. The high
efficiency equipment available today utilizes a lower head
pressure than earlier manufactured air conditioning systems
including indoor heat exchangers consequently to replace only the
compressor and condenser requires additional apparatus to achieve
the highest efficiency available for the system. This integration
of equipment, as disclosed herein, includes the use of the flash
subcooler arrangement for subcooling refrigerant flowing to the
evaporator. The subcooling of the refrigerant flowing to the
evaporator acts to allow the capillary tubes of the evaporator to
maintain a mass flow rate of refrigerant notwithstanding a lower
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head pressure. This is accomplished by subcooling a portion of
the liquid refrigerant entering the evaporator such that the
capacity of the unit may be maintained at the lower head pressure.
Many of the existing evaporators designed to have a lesser flow
rate utilize capillary tubes as an expansion device. The amount
of refrigerant which may flow through a capillary tube is a
function of pressure and temperature of the refrigerant. Since
the temperature of the liquid refrigerant leaving the condenser is
limited by air temperature in an air cooled application, raising
the pressure has been a conventional method of improving feeding
to an evaporator. Increasing the pressure can be achieved by
adding more charge of refrigerant to the system. However, after a
certain point of increasing charge degradation of performance will
occur due to excessive liquid being stored in the condenser which
minimizes effective coil surface.
Consequently, by flash subcooling the refrigerant supplied to the
evaporator, the temperature rather than the pressure of the
refrigerant is affected and a high efficiency system may be
maintained without increasing the head pressure. Additionally, in
any fixed orifice metering device there is a problem of starving
and flooding at conditions other than design point. The addition
of the thermal expansion valve of the flash subcooler in
combination with the metering device acts to provide some
flexibility in the system to provide for optimum performance.
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